Field of the Invention
It is already known to add sodium salts of sulfonated melamine-formaldehyde resins to inorganic materials for construction, in order to improve their workability and their stability development.
For the practice the resins known up to now may not be prepared in the desired high concentration. Already at a solid content of more than 35% the resins show an unserviceable high viscosity, which still increases when the resins are stored. These resins are not suitable as salts of multivalent cations because they are insoluble. Due to the high dosage of these resin solutions from 1 to 5%, referred to the binding agent mixture, high portions of alkalis reach the material for construction. The negative influence of alkalis on the stability development, the shrinkage and especially the reactivity with certain silicatic additive materials are known. For this reason in West Germany the expert committee on "Betonzusatzmittel" ("concrete additive agents") determined the alkali content for additive agents in the case of danger of disadvantageous reactions in concrete to a maximum of 0.02% Na.sub.2 O, referred to the binding agent.
Known testing prescriptions are e.g. in the U.S.A. the ASTM standards C 295, C 227 and C 289.